Human-computer interface system having a 3d gaze tracker

ABSTRACT

An apparatus for interfacing a person with a computer, the apparatus comprising a gaze tracker having a 3D camera and a picture camera that image the person and a controller that processes images acquired by the cameras to determine a gaze direction and point of regard of the person.

RELATED APPLICATIONS

The present application is a continuation-in-part of U.S. patentapplication Ser. No. 12/965,948 filed Dec. 13, 2010, which isincorporated herein reference.

TECHNICAL FIELD

Embodiments of the invention relate to methods and apparatus fortracking a person's gaze and “point of regard” (POR) to which the gazeis attended, and systems that use the methods and apparatus to interfacea person with a computer.

BACKGROUND

Various types of eye tracking, or gaze tracking, systems for determininga direction of a person's gaze and what the person is looking at, areknown in the art. The systems are used, by way of example, for ergonomicand medical research, diagnostics, and interfacing a person with acomputer, or a computer generated artificial environment.

Generally, the systems operate to determine a location for the person'spupil, and a gaze direction along which the person is looking, which isdefined as a direction of a “gaze vector” that extends out from the eyealong a line from a center of rotation of the eye through the center ofthe located pupil. A location of the eye in three-dimensional (3D) spaceis determined and used to determine coordinates of a region of spacethrough which the gaze vector passes. The determined coordinates of theregion, hereinafter referred to as an “origin” of the vector, locate thegaze vector in space. Given the direction and origin of the gaze vector,its intersection with a region or object in the person's environment isidentified to determine what the person is looking at, which,presumably, is a point regard (POR) to which the person's attention isdirected.

Hereinafter, a POR, is assumed to be coincident with an intersection ofa person's direction of gaze and an object or region in the person'senvironment, and is used to refer to the intersection, object, orregion. A gaze tracking system, hereinafter referred to as a “gazetracker”, provides both a direction and an origin for a person's gazevector, and optionally a POR, for the person.

Intrusive and non-intrusive methods and gaze trackers exist fordetermining a direction for a gaze vector. In some intrusive gazetrackers a person wears special contact lenses comprising inductionmicro-coils that move with the eye and pupil. A high frequencyelectromagnetic field is used to track orientation of the micro-coilsand thereby the person's eyes and direction of gaze. In some intrusivegaze trackers, a person is fitted with electrodes that sense changes inorientation of a dipole electric field that the eye generates todetermine direction of gaze.

Non-intrusive gaze trackers and tracking methods often imagereflections, referred to as “Purkinje reflections”, of light fromsurfaces of different structures of the eye and process images of thereflections to determine their relative motion, and therefrom changes indirection of a person's gaze. The changes in gaze direction arereferenced to a reference gaze direction to determine the person's gazedirection. First, second, third, and fourth Purkinje reflections referrespectively to reflections from the front surface of the cornea, fromthe back surface of the cornea, the front surface of the lens and theback surface of the lens.

For a given stationary source of light, reflections from the frontsurface of the cornea, the first Purkinje reflection, are strongest andare conventionally referred to as “glints”. Locations of images ofglints are relatively independent of direction of gaze for moderate eyerotations (eye rotations up to about ±15°) and a fixed position of thehead. Locations of images of glints are typically used to referencemotion of images of features of the eye or of other Purkinje reflectionsto determine changes in a person's gaze direction.

In many non-intrusive gaze trackers, changes in location of an image ofthe pupil relative to an image of a glint are used to determine gazedirection. In some non-intrusive gaze trackers, reflections of lightfrom the retina, which are not usually classified as a Purkinjereflections are used to image the pupil and track eye motion and gazedirection. The retina acts like a retro reflector and light that entersthe pupil and is reflected by the retina exits the pupil along adirection that it entered the eye and backlights the pupil. The retinalbacklighting of the pupil produces the familiar “bright eye”, or “redeye” effect, frequently seen in images of people's faces acquired with aflash. Bright eye pupil images of a person are acquired by a camerausing light sources that illuminate the person's face from a directionsubstantially coincident with the camera optic axis. Locations of thebright eye pupil in the images are tracked relative to locations ofglints in the images to determine the person's gaze direction. Brighteye pupil images are not produced by off axis light sources, and for offaxis light sources, an imaged pupil appears dark. In many non-intrusivegaze trackers, locations of “dark pupil images” are compared tolocations of images of glints to determine direction of gaze.

For many applications of a gaze tracker, a person's head is required tobe stabilized relative to components of the gaze tracker so that it canprovide acceptably accurate determinations of a direction and an originfor a gaze vector, and therefrom a POR for the person. For some gazetrackers, the person's head is stabilized by a static support, such as achin rest often used in ophthalmic examinations, or a bite bar, to fixthe head and eyes relative to components of the gaze trackers.

For applications such as interfacing a person with a virtual oraugmented reality, it is advantageous for the person to be able tofreely move his or her head and for these applications, a persontypically wears a headgear, such as a helmet or goggles, that comprisesgaze tracker components. The headgear holds the gaze tracker componentsin substantially fixed locations relative to the person's head andprovides fixed, known, distances and orientations of the eye relative tothe components. The known distances and orientations facilitatedetermining gaze vector directions and origins for the person relativeto the headgear. Gaze vector directions and origins relative to the realworld, a virtual or augmented reality, are determined from the gazedirections and origins relative to the headgear, and orientation of theheadgear in the real world. Orientation of the headgear is determinedusing any of various optical, electromagnetic or mechanical position andorientation sensor systems.

Some gaze trackers provide directions and origins of gaze vectors andPORs for a person without recourse to a worn headgear. However, thesegaze trackers generally operate for head positions restricted to arelatively small range of distances between about 50 cm (centimeter) andabout 80 cm from the gaze trackers.

SUMMARY

An embodiment of the invention provides a three-dimensional (3D) gazetracker and a system that uses the 3D gaze tracker to interface a personwith a computer. The 3D gaze tracker determines gaze vectors for aperson who is substantially unencumbered by gaze tracking headgear andenjoying freedom of motion in a field of view (FOV) of the gaze trackerhaving a depth of field that extends to a relatively large distance fromthe tracker. Optionally, the gaze tracker determines a POR for gazevectors that it determines. In an embodiment of the invention, thecomputer may generate images on a video display to interact with theperson and the 3D gaze tracker, or a processor that receives datadefining the POR determined by the 3D gaze tracker, generates an iconindicating location of the POR on the video display.

In an embodiment of the invention, the 3D gaze tracker comprises a 3Dcamera, which acquires range images of the person that provide 3Dspatial coordinates for features of the person's face and/or head, and acamera, hereinafter also a “picture camera”, which acquires contrastimages, hereinafter “pictures”, of the features. A processor processesthe contrast and range images to distinguish the person's eyes andfeatures of the eyes, for example, an eye glint a bright or dark pupil,and features of the face or head, such as the nose, chin or forehead,and determines 3D spatial coordinates for the features. The processorprovides directions and origins for gaze vectors for the person, andoptionally PORs associated with the gaze vectors, responsive to thedistinguished features, and their 3D spatial coordinates.

Optionally, the 3D camera comprises a time of flight (TOF) 3D cameraconfigured to provide range images in a FOV that extends to a distancebetween at least 1 m (meter) and 3 m from the gaze tracker. Optionally,the FOV extends from a distance equal to about 30 cm from the gazetracker.

In the discussion, unless otherwise stated, adverbs such as“substantially” and “about” modifying a condition or relationshipcharacteristic of a feature or features of an embodiment of theinvention, are understood to mean that the condition or characteristicis defined to within tolerances that are acceptable for operation of theembodiment for an application for which it is intended. Unless otherwiseindicated, the word “or” in the specification and claims is consideredto be the inclusive “or” rather than the exclusive or, and indicates atleast one of, or any combination of items it conjoins.

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used to limit the scope of the claimed subject matter.

BRIEF DESCRIPTION OF FIGURES

Non-limiting examples of embodiments of the invention are describedbelow with reference to figures attached hereto that are listedfollowing this paragraph. Identical structures, elements or parts thatappear in more than one figure are generally labeled with a same numeralin all the figures in which they appear. Dimensions of components andfeatures shown in the figures are chosen for convenience and clarity ofpresentation and are not necessarily shown to scale.

FIG. 1A schematically shows a 3D gaze tracker comprising a TOF 3D cameradetermining gaze vectors and a POR for a person, in accordance with anembodiment of the invention;

FIG. 1B schematically shows the 3D gaze tracker shown in FIG. 1A beingused in a video game, in accordance with an embodiment of the invention;

FIGS. 2A-2C schematically illustrate relationships between the pupil ofan eye and a glint as a function of gaze angle that may be used by a 3Dgaze tracker, in accordance with an embodiment of the invention;

FIGS. 3A-3C schematically illustrate aspects of head orientation ondetermination of gaze direction;

FIG. 4 schematically shows a 3D gaze tracker that concentrates light ona person's head to acquire range images and pictures for determining agaze direction and POR for the person, in accordance with an embodimentof the invention;

FIG. 5 schematically illustrates aspects of determining an origin for agaze vector of an eye and its associated POR responsive to distance ofthe eye from a gaze tracker, in accordance with an embodiment of theinvention; and

FIG. 6 schematically shows a 3D gaze tracker comprising a stereoscopic3D camera determining gaze vectors and a POR for a person in accordancewith an embodiment of the invention;

DETAILED DESCRIPTION

In the detailed description below aspects of embodiments of theinvention are discussed with respect to a 3D gaze tracker schematicallyshown in FIGS. 1A and 1B, which comprises a TOF 3D camera, and a picturecamera, in accordance with an embodiment of the invention. Aspects ofdetermining gaze directions responsive to images of eye glints andpupils acquired by the 3D gaze tracker, in accordance with an embodimentof the invention, are discussed with reference to FIGS. 2A-2C. Effectsof head orientation on determining gaze directions, and aspects ofdetermining head orientations and gaze directions by the 3D gaze trackerin accordance with an embodiment of the invention are illustrated anddiscussed with reference to FIGS. 3A-3C. A variation of a 3D gazetracker that tracks a person with a cone of light to provide enhancedillumination of the person, in accordance with an embodiment of theinvention, is discussed with reference to FIG. 4. Determinations of gazevector origins using range images acquired by a 3D gaze tracker inaccordance with an embodiment of the invention are discussed withreference to FIG. 5. FIG. 6 schematically shows an embodiment of a 3Dgaze tracker comprising a stereoscopic 3D imager that determinesdistances by triangulation.

FIG. 1A schematically shows a 3D gaze tracker 20 imaging a person 22whose head is located within a field of view (FOV) 30 of the 3D gazetracker, in accordance with an embodiment of the invention. The gazetracker is tracking the person's gaze by determining gaze vectors andPORs for the person as he or she moves around, and engages inactivities, in the FOV. A dashed line 61 represents an optical axis ofthe 3D gaze tracker, and dashed lines 32, 34, and 36, outline a frustumdelimiting a volume of FOV 30. The FOV has a depth of field extendingfrom 3D gaze tracker 20 having a minimum, lower bound rangeschematically indicated by location of a plane defined by dashed lines32, and a maximum, upper bound range schematically indicated by locationof a plane defined by dashed lines 36.

In some embodiments of the invention, the lower bound range is equal toor greater than about 30 cm. Optionally, the lower bound range is equalto or greater than about 50 cm. In some embodiments of the invention,the upper bound range is greater than or equal to about 1 m. Optionally,the upper bound range is equal to or greater than about 2 m. In someembodiments of the invention, the upper bound range is equal to about 3m.

A view angle of 3D gaze tracker 20 is a largest possible angle betweenlines that lie in FOV 30 and a plane through optical axis 61. Horizontaland vertical view angles are view angles for horizontal (parallel to theground) and vertical (perpendicular to the ground) planes respectivelythat contain optical axis 61. In some embodiments of the invention, atleast one of the horizontal and vertical view angles is equal to orgreater than about 45°. Optionally, at least one of the view angles isequal to or greater than 90°. In some embodiments of the invention, atleast one of the view angles is equal to about 120° or 150°.

By way of example, 3D gaze tracker 20 is assumed to be tracking the gazeof person 22 to interface the person with a computer (not shown) via avideo display 40. Video display 40 may be any of various video displays,such as by way of non-limiting example, a desk top computer screen, avideo game console screen, a tablet screen, or a smartphone screen. Thecomputer, also referred to as the “video display computer”, may be anyprocessing device or system, such as by way of non-limiting example, agaming console configured to support online video gaming, a laptop,smartphone, or tablet, that uses video display 40 to interface withperson 22.

Block arrows 42 in FIG. 1A schematically represent gaze vectors forperson 22, and dashed lines 43 indicate their directions as convergingto a POR 44 at the lower left corner of video display 40. A controller24 controls 3D gaze tracker 20 and may be interfaced with the videodisplay computer by a suitable application programming interface (API)so that information generated by the 3D gaze tracker is applicable toimages displayed on video display 40 and may be used to modify theimages. Modifying the displayed images comprises effecting any change tothe displayed images, and comprises by way of example, making a changeto the images themselves or adding information to the images.

It is noted that whereas in the above description controller 24 may beunderstood to be separate from the video display computer, controller 24may be integrated with, comprise, or be comprised in the video displaycomputer and may be implemented using any combination of hardware orsoftware components. Controller 24, as well as the video displaycomputer may for example, and without limitation, comprise anapplication specific integrated circuit (ASIC), a field programmablegate array (FPGA) or a system on a chip that may store and execute aninstruction set that provides a functionality of 3D gaze tracker 20 orthe video display computer. Controller 24 may comprise a general purposeprocessor having access to, or including a computer readable memorystoring an executable instruction set which the processor executes toprovide a functionality of 3D gaze tracker 20 or the video displaycomputer. Controller 24 may be configured as a distributed system,optionally implemented in the cloud, having various functionalities thatcommunicate with each other to cooperate in performing tasks of 3D gazetracker 20.

In an embodiment of the invention, controller 24 generates informationthat the API uses to indicate on video display 40 a location of POR 44.Optionally, controller 24 provides information that defines a region ofuncertainty (ROU) for the location of POR 44 determined by 3D gazetracker 20. For example, location of POR 44 may be visibly indicated onvideo display 40 by a suitable “POR icon”, which as schematically shownin FIG. 1A may be a circle 45. Diameter of circle 45 may indicateaccuracy, a ROU, with which the 3D gaze tracker 20 determines locationof POR 44.

The location of POR icon 45 provides visual feedback for person 22 whichthe person may use to adjust a location for his or her POR in responseto displays generated on video display 40. For example, 3D gaze tracker20 may be used to enable person 22 to interact with a video gamepresented on video display 40 by the video display computer. As anillustrative non-limiting example, the video game might be an aerialdogfight video game schematically shown in FIG. 1B, in which person 22attempts to follow a maneuvering enemy fighter 91 with her eyes tocenter her POR 44 on the fighter. When person 22 sees that her POR 44 asindicated by circle 45 is centered on enemy fighter 91 she may operate,optionally, a joystick (not shown) to release an air to air missile (notshown) or fire a canon (not shown) to destroy the enemy fighter.

The 3D gaze tracker optionally comprises a light source 50 controllableby controller 24 to radiate a train 51 of light pulses, schematicallyrepresented by square “pulses” labeled with a numeral 52, to illuminateobjects and people in FOV 30, and by way of example in FIGS. 1A and 1B,person 22. Numeral 52 is also used to refer to the light pulses. Whereaslight pulses 52 may comprise light from any portion of the spectrumprovided by a suitable light emitting diode (LED) and/or laser, usuallythe light pulses are vision safe, near infrared (NIR) light pulses.

An optical system, represented by a lens 60 having an optical axis thatcoincides with optical axis 61, comprised in 3D gaze tracker 20 collectslight from light pulses 52 that is reflected back to the 3D gaze trackerby features of person 22, and directs the collected light to a beamsplitter 62. Light that beam splitter 62 receives from lens 60 isschematically represented by a block arrow 64, and the numeral 64 isused to reference the light.

Beam splitter 62 directs, optionally about one-half, of the light itreceives from lens 60 to a photosensor 70, hereinafter also referred toas a “range photosensor 70”, having light sensitive pixels 72 (FIG. 1A).Light that beam splitter 62 directs to range photosensor 70 isrepresented by a block arrow 74 and the numeral 74 is used to referencethe light. Photosensor 70 is shuttered open or closed to respectivelyenable it to register light 74 or prevent it from registering the light.Optionally, as schematically shown in FIG. 1, shuttering is accomplishedby a shutter 76 located between beam splitter 62 and photosensor 70 thatis controlled by controller 24 to prevent or enable light 74 directedtowards the photosensor by beam splitter 62 to propagate to thephotosensor. In some embodiments, turning on and turning off thephotosensor respectively accomplish shuttering the photosensor open andclosed.

Following a predetermined delay from a time at which each light pulse 52in the train of light pulses is radiated by light source 50 toilluminate person 22, controller 24 controls shutter 76 to shutter openphotosensor 70 for a short exposure period. Light 74 that reaches 3Dgaze tracker 20 during the exposure period is transmitted by shutter 76and imaged onto photosensor 70 for registration by pixels 72 in thephotosensor. An amount of light 74 registered by a given pixel 72 duringthe short exposure period is a portion of a total amount of light 74reflected from the light pulse by a feature imaged on the pixel anddirected towards photosensor 70 by beam splitter 62. The amount is afunction of a distance of the feature from 3D gaze tracker 20.

The amounts of light reflected by features of person 22 from the lightpulses in light pulse train 51 that are registered by pixels 72 providesa range image of the person. Controller 24 uses the amounts of lightregistered by the pixels to determine how long it takes light from lightpulses 52 to travel round trip from light source 50 to the person'sfeatures respectively imaged on the pixels and back to 3D gaze tracker20. The controller determines distances from the 3D gaze tracker of thefeatures from the speed of light and the round trip times.

Light reflected by features of person 22 that is collected by opticallens 60 and not directed by beam splitter 62 to photosensor 70 isdirected by the beam splitter to a photosensor 80, hereinafter referredto as a “picture photosensor 80”, having pixels 82. A block arrow 84schematically represents light directed by beam splitter 62 to picturephotosensor 80, and the numeral 84 is used to reference the light.Optionally, a shutter 86 located between beam splitter 62 and picturephotosensor 80 shutters the photosensor. Unlike range photosensor 70however, picture photosensor 80 is shuttered open for relatively longexposure periods, sufficiently long so that substantially all the lightreflected from a pulse 52 that is collected by 3D gaze tracker 20 anddirected by beam splitter 62 to picture photosensor 80 (that is, light84) is registered by the picture photosensor. Picture photosensor 80therefore provides a contrast image 88, hereinafter also referred to asa “picture 88”, of person 22, similar to conventional pictures acquiredby a camera.

Whereas, generally a picture of person 22 imaged on picture photosensor80 includes a picture of the person's head, and objects and possiblyother people in the near vicinity of the person, for convenience ofpresentation, only eyes 100 of person 22 are shown in picture 88.

Controller 24 processes picture 88 using any of various patternrecognition algorithms to identify and locate an image of an eye 100 inthe picture and identify at least one feature of the eye that is useablefor determining a direction of gaze vector 42 associated with the eye.The at least one eye feature comprises at least one of the pupil, theiris, a boundary between the iris and the sclera, and a glint generatedby light reflected off the eye. An enlarged image of eye 100 imaged by3D gaze tracker 20 on picture photosensor 80 is schematically shown inan inset 110 in FIG. 1A. A glint 101, a pupil 102, an iris 103, sclera104, and a boundary 105 between the sclera and iris are schematicallyshown for the eye in the inset. Controller 24 determines a direction ofa gaze vector for the eye responsive to the at least one identified eyefeature.

By way of example, in an embodiment of the invention, controller 24determines gaze vector direction for an eye 100 of person 22 fromlocations of glint 101 and pupil 102 in the image of an eye 100 inpicture 88. FIGS. 2A-2C schematically show relationships betweenfeatures of eye 100 that may be used in an embodiment of the inventionfor determining gaze direction for person 22 responsive to images ofglint 101 and pupil 102 of the eye.

FIGS. 2A and 2B show a schematic circular cross section 120 of an eye100, assumed to be a sphere having a surface 121, center of rotation124, an iris 103, and a pupil 102 having a center 122 located at adistance “d_(P)” from center of rotation 124. Whereas the eye is not aperfect sphere, but is slightly ovate with a bulge at the location ofthe cornea, modeling the eye as a sphere provides qualitative andquantitative insight into aspects of determining gaze direction.Typically, the eye has a diameter equal to about 24 mm (millimeters) andd_(p) is equal to about 10 mm.

In FIGS. 2A and 2B a camera 130 comprising a lens 131 and a photosensor132 is shown imaging eye 100. Functioning of camera 130 in imaging eye100 simulates imaging of eyes 100 of person 22 by lens 60 (FIG. 1A) andpicture photosensor 80 in 3D gaze tracker 20. Principles of the imagingthat apply to camera 130 also apply to imaging of the eyes by 3D gazetracker 20.

In FIG. 2A, center of rotation 124 of eye 100 is assumed by way ofexample to be located along an optical axis 135 of camera 130 and theeye is assumed to be illuminated by light, represented by a block arrow136 that is coaxial with the optical axis. The light is reflected bysurface 121 of eye 100 to generate a glint 101 at an intersection 123 ofthe optical axis and the eye surface. The glint is imaged on aphotosensor 132 with a center of the glint image located at anintersection 137 of optical axis 135 and the photosensor. A circle 138at intersection 137 schematically represents the image of glint 101.

In the figure, a gaze of eye 100 is assumed to be directed towardscamera 130 along optical axis 135. As a result, pupil 102 is alignedwith glint 101 and center 122 of the pupil lies on optical axis 135.Pupil 102 is imaged on photosensor 132 with the center of the pupilimage located at intersection 137 and coincident with the center ofimage 138 of glint 101. The image of pupil 102 is schematicallyrepresented by a filled circle 140 located to the left of circle 138representing the image of glint 101.

FIG. 2B schematically shows eye 100 being imaged as in FIG. 2A, but withthe eye and its gaze direction rotated “upwards” by an angle θ. As aresult, whereas glint 101 has not moved, pupil 102 is no longer alignedwith glint 101 along optic axis 135. Center 122 of pupil 102 is locateda distance Δ=d_(P) sin θ from optic axis 135 and image 140 of the centerof pupil 102 is no longer located at intersection 137 and no longercoincident with the center of glint 101.

If magnification of camera 130 is represented by “M”, centers of images138 and 140 of glint 101 and pupil 102 are separated by a distanceΔ_(I)=MΔ=Md_(P) sin θ. Gaze direction θ of eye 100 can be determinedfrom a relationship sin θ=(Δ_(I)/Md_(P)). In practice, images of a pupiland a glint are generally not perfect circles, and typically Δ_(I) isdetermined as a distance between centroids of images of the pupil andthe glint.

FIG. 2C shows schematic images 150 of eye 100, and in each image showsimages of glint 101, pupil 102, iris 103 and sclera 104 for the eye,acquired by camera 130 (FIGS. 2A and 2B) for rotations of the eye by asame angle θ about different axes through center of rotation 124 of theeye. All the images are associated with a same position of center ofrotation 124 along optical axis 135 (FIGS. 2A and 2B).

A central image 151 corresponds to an image acquired for eye 100 for theorientation of the eye shown in FIG. 2A, for which there is no rotation(θ=0) of the eye, and glint 101 is aligned with pupil 102 along opticalaxis 135. Each of the other eye images 150 is associated with an axis160 of rotation about which the eye in the image and direction of gazeof the eye is rotated by same angle θ. The axis of rotation passesthough the center of rotation 124 (FIGS. 2A and 2B) of the eye, isparallel to the plane of FIG. 2C, and is associated with a circle arrow161 indicating direction of rotation of the eye about the axis.Direction of gaze for each image 150 of the eye relative to the gazedirection of central image 151 along optical axis 135 (FIGS. 2A and 2B),is schematically indicated by a block arrow 163. For each differentrotation of eye 100 and its associated direction of gaze, orientation ofglint 101 and pupil 102 is different, and the orientation and distancebetween the centers of the glint and pupil may be used to determinedirection of gaze of person 22.

It is noted that embodiments of the invention, are not limited todetermining gaze direction in accordance with the discussion above. Forexample, an embodiment may determine gaze direction of a person byprocessing images of his or her eyes to determine centers or centroidsof their irises rather than centers or centroids of the pupils. Theembodiment may use a location of the centers or centroids of the irisesrelative to a centroid or center of a glint to determine gaze direction.In some embodiments, direction of gaze of an eye is determined from adistribution in an image of the eye of regions determined to belong tothe eye's sclera (referenced by numeral 104 in FIGS. 1, and 2C) relativeto regions that are determined to belong to the iris. In someembodiments relative motion of Purkinje reflections, in particular theglint and the fourth Purkinje reflection, which is a reflection from theback of the eye lens, is used to determine direction of gaze.

FIGS. 2A-2C, and the above description of the Figs. provide a verysimplified exposition of a method of determining gaze direction fromimages of glints and pupils. In practice, determining eye direction fromimages of pupils and glints generally comprises accounting for headmotion, differences in the eye structure of different individuals, and,advantageously, calibrating images of eyes with eye gaze directions.

Influence of head orientation on gaze direction and limitations ofdetermining gaze direction responsive only to relative positions of thepupil of an eye and the glint are illustrated for a simplified set ofcircumstances in FIG. 3A-FIG. 3C.

All the figures show, very schematically, on a left side of the figure,a perspective view of a camera 130 imaging a person 22 to acquirepictures of the person's eye 100 for determining his or her direction ofgaze responsive to relative positions of a glint 101 and pupil 102 inthe acquired pictures. An arrow 170 in FIGS. 3A, 3B and 3C points fromthe schematic perspective view in the figure to a schematic picture 171,172, and 173 respectively, of the person acquired by camera 130.

In FIG. 3B, camera 130 is assumed to be directly in front of person 22,with its optic axis 135 aligned with and pointing at the person's nose.The person is looking slightly upward along a direction indicated by ablock arrow 182. In picture 172 of the person acquired by camera 130,glint 101 is therefore directly below pupil 102. The relative positionsof the glint and pupil indicate the alignment of the person with thecamera and the slightly upward direction of the person's gaze.

In FIG. 3A the only change in the relative positions of camera 130 andperson 22 is that the person's head is rotated clockwise in a directionindicated by a circle arrow 174, about an axis 175 that passes throughthe center of pupil 102 and the center of glint 101. As a result, theperson is looking along a direction indicated by a block arrow 181 thatis rotated with respect to the gaze direction indicated by block arrow182 in FIG. 3B. However, whereas the gaze direction of the person inFIG. 3A is different from that in FIG. 3B, relative locations of pupil102 and glint 101 in picture 171 of the person in FIG. 3A are the sameas those in picture 172 of the person in FIG. 3B. The relative locationsare the same because the head is rotated about an axis through the pupiland glint.

In FIG. 3C, the only change in the positions of camera 130 and person 22relative to their positions in FIG. 3B is that the person's head isrotated counterclockwise in a direction indicated by a circle arrow 176about axis 177 by an angle equal in magnitude, but opposite in directionto that of the rotation angle in FIG. 3A. A block arrow 183 indicatesdirection of gaze of person 22 in FIG. 3C. Whereas direction of gazeindicated by block arrow 183 is different from gaze directions indicatedby block arrows 181 and 182, location of pupil 102 relative to glint 101in picture 173 is the same as in pictures 171 and 172.

For the conditions noted in the discussion of FIGS. 3A-3C, the images ofglint 101 and pupil 102 in FIGS. 171, 172 and 173 do not distinguish thegaze directions represented by block arrows 181, 182 and 183. Withoutadditional information, such as orientation of the person's head inFIGS. 3A-3C, glint 101 and pupil 102 acquired by camera 130 bythemselves do not disambiguate gaze directions indicated by the blockarrows. Images of the person's features, for example images of directionof the nose, in pictures 171, 173 and 174 may provide additionalinformation useable to determine a direction of the person's head anddifferentiate the gaze directions.

In an embodiment of the invention, controller 24 processes range imagesacquired by range photosensor 70 and/or pictures of person 22 shown inFIGS. 1A and 1B acquired by picture photosensor 80 to determine headorientation of person 22 for use in determining gaze directions of theperson.

For example, in an embodiment of the invention, controller 24 processesrange images of person 22 to determine distances from 3D gaze tracker 20of features, hereinafter referred to as “fiducial features”, of theperson's head that may advantageously be used to indicate orientation ofthe head. Fiducial features may include facial features such as theforehead, eyes, tip of the nose, lips and chin, and the ears. Distancesof the eyes, cheekbones, or ears of person 22 from the 3D gaze trackermay be used to determine an azimuthal angle of the person's head. Anazimuthal angle is an angle about an axis through the person's head thatis perpendicular to the ground when the person is standing upright withthe head. A tilt angle of the head about an axis through the ears, whichaxis is parallel to the ground when the person is standing upright maybe determined responsive to distance from 3D gaze tracker 20 of theperson's forehead and chin.

In an embodiment of the invention, fiducial features are identifiedresponsive to their images in a picture acquired by picture photosensor80 (FIGS. 1A and 1B). Distances to the fiducial features imaged onpixels 82 in picture photosensor 80 are determined from distancesprovided by corresponding pixels 72 in range photosensor 70 on whichlight from the fiducial features is imaged.

To facilitate determining correspondence of pixels 72 in rangephotosensor 70 with pixels 82 in picture photosensor 80, optionally, thephotosensors are configured having equal size pixels and are positionedand mounted in 3D gaze tracker 20 so that homologous pixels image sameregions in FOV 30.

In some embodiments of the invention, pixels 72 and pixels 82 may havedifferent sizes. For example, generally, intensity of light in lightpulses 52 is limited by cost considerations and heat dissipationrequirements for maintaining light source 50 (FIGS. 1A and 1B) andcomponents of 3D gaze tracker 20 at acceptable operating temperatures.In addition, durations of the light pulses and exposure periods providedby shutter 76 are relatively short and may be less than 10 or 20 ns(nanoseconds). Amounts of light from light source 50 reflected by person22 that are available per pixel 72 of range photosensor 70 for acquiringa range image of the person may therefore be limited. As a result, forpixels 72 in range photosensor 70 to register quantities of lightsufficient to provide signals having acceptable signal to noise ratios(SNRs), it can be advantageous for the pixels to be relatively large. Inan embodiment of the invention therefore, pixels 72, which are typicallysquare, may advantageously have side dimensions greater than about 10μ(microns).

On the other hand, because exposure periods of picture photosensor 80may be at least three times longer than exposure periods of rangephotosensor 70, more light is generally available for imaging a personon picture photosensor 80 than for imaging the person on rangephotosensor 70. To resolve distances between a glint and the pupil of aneye, pixels 82 in picture photosensor 80 are therefore advantageouslyrelatively small.

In general, a maximum change in a distance between a glint and the pupilof an eye per degree of rotation of the eye is about 0.17 mm, if onlythe eye rotates and the glint is localized to the cornea. For example,for a 1° of change in angle θ of direction of a person's gaze, distanceΔ in FIG. 2B relative to optical axis 135 in the figure changes by about0.17 mm. If 3D gaze tracker 20 images person 22 at a magnification ofabout 10⁻² on picture photosensor 80, to resolve changes of about 2° inθ responsive to changes in distance between pupil 102 and glint 101,pixels 72 in the picture photosensor are advantageously less than orequal to about 2.5μ on a side.

In some embodiments for which pixels 72 and 82 differ in size, range andpicture photosensors 70 and 80 are aligned so that the larger pixels inone of the photosensors are substantially homologous with tiles ofsmaller pixels in the other of the photosensors and image same regionsof FOV 30 that their homologous tiles image. For example, in anembodiment of the invention for which pixels 72 in range photosensor 70are 10μ along a side and pixels 82 in picture photosensor 80 are 2.5μalong a side, large pixels 72 in range photosensor 70 may be homologouswith square tiles comprising 16 small, 2.5μ pixels 82 in picturephotosensor 80.

In some embodiments of the invention to accommodate differentrequirements and constraints of imaging on range photosensor 70 andpicture photosensor 80, 3D gaze tracker 20 comprises optics foradjusting magnification of imaging on the photosensors independently ofeach other.

For example, an embodiment of the invention may comprise opticalelements, such as zoom lens optics (not shown) located between beamsplitter 62 and picture photosensor 80 that controller 24 controls toadjust magnification of images of person 22 formed on the picturephotosensor. For situations in which person 22 is far from 3D gazetracker 20, the controller optionally controls the zoom lens optics tozoom in on the person and magnify an image of eyes 100 and distancesbetween glints 101 and pupils 102 in the image. The increasedmagnification improves accuracy with which distances between glints andpupils, and thereby gaze directions, are determined. In an embodiment ofthe invention, controller 24 controls magnification of images on picturephotosensor 80 responsive to distances to person 22 provided by rangeimages acquired by range photosensor 70, and increases and decreasesmagnification as images acquired by the range photosensor indicateincrease and decrease respectively in distance of person 22 from 3D gazetracker 20.

In some embodiments of the invention, controller 24 controls intensityof light in light pulses 52 responsive to distance measurements providedby range photosensor 70. As person 22 moves farther from or closer to 3Dgaze tracker 20, the controller respectively increases and decreasesintensity of light in light pulses 52. Adjusting light intensity as afunction of distance can improve efficiency with which light from lightsource 50 is used. For constant intensity of light transmitted by lightsource 50, SNR of signals provided by pixels 72 for determining distanceof features of person 22 is inversely proportional to the square of thedistance of the person from 3D gaze tracker 20. Increasing illuminationwith distance can compensate, at least partially, for decrease inintensity of illumination of person 22 as the person moves away from 3Dgaze tracker 20.

In some embodiments of the invention, light source 50 is controllable todirect light pulses 52 into a cone, hereinafter an “illumination cone”,having a desired direction and solid angle to concentrate light in alimited region in FOV 30 and improve efficiency with which light formthe light source is used to illuminate person 22. In an embodiment ofthe invention, controller 24 controls direction and solid angle of thecone responsive to location of the face and head of person 22 in FOV 30determined from images acquired by range photosensor 70 and/or picturephotosensor 80 to concentrate light on the person's face, or a portionthereof. By illuminating a limited region of FOV 30 that contains thehead of person 22, or a portion of the head, such as a portioncomprising the eyes, intensity of light available for imaging the headand/or eyes can be increased, and accuracy of gaze vector determinationimproved.

FIG. 4 schematically shows a 3D gaze tracker 320 similar to 3D gazetracker 20 shown in FIGS. 1A and 1B generating and directing anillumination cone 322, shown shaded, to concentrate light in a limitedportion of FOV 30 to illuminate the head and face of a person 22, inaccordance with an embodiment of the invention. A portion ofillumination cone 322 is outlined by dashed lines 323 that extend fromlight source 50 to corners of an optionally square illumination area “A”outlined by dashed lines 324.

Area A is an area illuminated by light from light pulses 52 and isassumed to be located at a distance “D” of person 22 from 3D gazetracker 320. Area A determines a solid angle, Ω, of illumination cone322 in accordance with an expression Ω=A/D². A is optionally independentof D and optionally constant, for any distance of person 22 D within FOV30. A is optionally determined so that in a time it takes 3D gazetracker 320 to acquire an image of person 22, the person cannotgenerally move his or her head fast enough from a location along acentral axis (not shown) of the illumination cone to move the head outof illumination cone 322.

Optionally, area A is a square area having a side length equal to about50 cm. Assuming that images of person 22 are acquired by 3D gaze tracker320 at a video rate of 30 images per second it requires about 30 ms(milliseconds) for the 3D gaze tracker to acquire an image. In 30 ms, aperson moving at 10 km (kilometers) per hour moves about 10 cm. A 50 cmby 50 cm square illumination area A is therefore generally sufficientfor defining a light cone that can be directed to track and providecontinuous, advantageous illumination of a person moving in FOV 30.

Any of various devices and methods can be used in practice of anembodiment of the invention to generate and control direction and solidangle of illumination cone 322. For example, the light source maycomprise an array of micro mirrors controllable to reflect and directlight provided by the light source into illumination cone 322.Optionally, the light source comprises a lens system, for example a zoomlens system having a focal point located at a light emitting element ofthe light source, for controlling the solid angle of illumination cone322. In some embodiments of the invention, the light source comprises amechanical system that rotates the light source to direct illuminationcone 322 to maintain person 22 within the illumination cone. In someembodiments of the invention, different light sources are turned on andoff to maintain person 22 within a small angle illumination cone as theperson moves around in FOV 30.

Except for the rare and generally uninteresting circumstance for which aperson looks directly at a camera that is imaging the person, gazedirection by itself is not sufficient to define a gaze vector for theperson and determine therefrom a POR. For most circumstances, threespatial coordinates (for example, x, y, and z coordinates of a Cartesiancoordinate system) of an origin for the gaze vector is required tolocate the gaze vector in space and determine a POR for the gaze vector.

In an embodiment of the invention, range images of a person, such asperson 22 in FOV 30 of 3D gaze tracker 20 (FIG. 1A), acquired by rangephotosensor 70 and/or pictures of the person provided by picturephotosensor 80 are processed by controller 24 to provide 3D spatialcoordinates for origins of the person's gaze vectors. In particular,distances from 3D gaze tracker 20 determined responsive to range imagesacquired by range photosensor 70 are used to provide a z-coordinate forthe origins. A z-coordinate is arbitrarily assumed to be a coordinatemeasured along a z-axis of an x,y,z, Cartesian coordinate system forwhich the z-axis is parallel to optical axis 61 (FIGS. 1A and 1B) of 3Dgaze tracker 20.

Whereas three spatial coordinates for a person's eye can usually beestimated from an image analysis of a picture of the person acquired bya camera, such estimates are generally practical for a limited range ofdistances from the camera, and are typically associated with relativelylarge margins of error. A TOF 3D camera, such as provided by rangephotosensor 70 and associated optics in 3D gaze tracker 20, can providespatial coordinates, and in particular a coordinate for distance fromthe 3D camera and therefore a z-coordinate of the eye relative to thecamera, having a relatively small margin for error.

FIG. 5 schematically shows a very simplified configuration thatillustrates how uncertainty in determining distance of a person's eyefrom a camera (not shown) that images the person generates uncertaintyin identifying a POR for the person from a gaze vector determined forthe eye. The figure shows an eye, schematically represented by anellipse 100, at three different collinear positions at differentdistances, indicated by witness lines 201, 202, and 203, from a videodisplay 40. The positions are arbitrarily defined to be the positions ofthe centers of rotation 124 of the eye and are located along a sameline, referred to as a “z-axis”, perpendicular to the video display. Thepositions indicated by the witness lines are referred to by the numerals201, 202, and 203 labeling the witness lines, and the eye is referred toby the numeral 100 labeling the ellipse representing the eye. Distanceof the eye from the camera imaging the eye is assumed to be the same asdistance of the eye from video display 40.

At each position 201, 202 and 203, the eye has a gaze vector 221, 222,and 223 respectively. Each gaze vector 221, 222, and 223 extends along adashed line 251, 252, and 253 respectively that passes from the eye'scenter of rotation 124 through the center of its pupil 102. All the gazevectors make a same inclination angle θ with the z-axis. Gaze vectors221, 222, and 223 intersect video screen 40 at intersection points 231,232, and 233 respectively, where dashed line 251, 252, and 253associated with the gaze vectors intersect the video screen.Intersections 231, 232, and 233 represent locations of PORs on videodisplay 40 that are determined from gaze vectors 221, 222, and 223respectively.

The eye is assumed to actually be located at “middle” position 202, andintersection 232 an actual POR for gaze vector 222 associated with theeye at the middle position. Positions 201 and 203 represent lower andupper bound estimates respectively for the z-coordinate of the eye thatmight reasonably result from image analysis of a picture that images theeye. A distance “ΔZ” between positions 201 and 203 represents anuncertainty in the z-coordinate of the eye determined from the imageanalysis. A concomitant uncertainty in where the actual POR is located,is represented by a “distance of uncertainty (DOU)” 236, betweenintersection points 231 and 233 on video display 40.

Z-coordinates indicated by witness lines 241 and 242 along the z-axisare referred to by numerals 241 and 242 and represent reasonable lowerand upper error bounds respectively in the z-coordinate of the eyedetermined by a TOF 3D camera. By way of example, witness lines 241 and242 may represent z-coordinate lower and upper error bounds,respectively, for the TOF 3D camera comprising light source 50, rangephotosensor 70 and associated optical elements in 3D gaze tracker 20.Distance “ΔZ*” between z-coordinates 241 and 242 represents anuncertainty in a z-coordinate for the eye determined by the TOF camera.

If eye 100 were located at 241, it is assumed that its gaze vector (notshown) would lie along a dashed line 257 that extends from point 241 atan angle θ with respect to the z-axis. The eye would be determined tohave a POR located at an intersection point 247 of dashed line 257 withvideo screen 40. Similarly, if eye 100 were located at position 242, itwould be determined to have a POR located at an intersection point 248of a dashed line 258 with video screen 40. The uncertainty generates acorresponding DOU 244, which is a distance between intersection points247 and 248. DOU 244 provided by the TOF 3D camera is generally smallerthan DOU 236 provided by image analysis alone.

By way of numerical example, assume that a person's eye 100 is locatedat a distance of about 50 cm from video display 40 and that the videodisplay has a diagonal dimension of about 60 cm so that a gaze angle θfor the eye may often be as large as 30°. An uncertainty ΔZ in az-coordinate for the person's eye provided by image analysis mayreasonably be assumed to be about 5 cm (±2.5 cm). The uncertaintyresults in an uncertainty, DOU 236, in the location of a POR for the eyethat may be estimated by the expression DOU 236=ΔZ tan θ, which for ΔZ=5cm and θ=30°, is equal to about 3 cm.

On the other hand, an uncertainty in the z-coordinate for the eyedetermined by a TOF 3D camera may reasonably be assumed equal to about 1cm (±0.5 cm) resulting in an uncertainty DOU 244 in the location of thePOR for θ=30° equal to about 0.6 cm. For example, assume a TOF 3D camerathat illuminates a FOV having a view angle of 45° with light pulseshaving intensity greater than or equal to about 50 milliwatts and pulsewidth between 15 and 20 ns that images objects in the FOV on aphotosensor comprising 10μ×10μ pixels. The camera can generally providedistance measurements characterized by z-coordinate accuracy equal toabout 1 cm for distance measurements between about 0.5 m and 3 m.

In an embodiment of the invention, to calibrate 3D gaze tracker 20 shownin FIGS. 1A and 1B (or 3D gaze tracker 320 FIG. 4), and adapt the 3Dgaze tracker to differences in eye structure and facial features ofdifferent users of the 3D gaze tracker, the 3D gaze tracker and displayon video display 40 are controlled to acquire calibration images of theusers.

In an embodiment, acquiring calibration images for a user, such asperson 22 shown in FIGS. 1A and 1B, comprises imaging the person foreach of a plurality of different “calibration positions” in FOV 30.Different calibration positions differ in distance from gaze tracker 20and/or location in FOV 30. For each calibration position, a range imageand a picture of the person are acquired for each of a plurality ofdifferent “calibration PORs” presented on video display 40 to which theperson's gaze is directed. Optionally, for a plurality of calibrationpositions, the person is requested to maintain his or her head in afixed position and move only the eyes to direct gaze at differentcalibration PORs.

The images are processed to provide 3D spatial coordinates for theperson's eye features, such as the pupil, iris, sclera, glints orPurkinje reflections, and/or fiducial features, for each of thecalibration positions and calibration PORs. The gaze vector for a givencalibration position and POR is optionally determined by 3D spatialcoordinates of the given calibration position and location of thecalibration POR on video screen 40. The eye feature and fiducial featurecoordinates, and associated gaze vectors, are stored as reference datain a suitable data array. In an embodiment of the invention, thereference data array is used to determine gaze vectors of person 22 asthe person moves around freely in FOV 30.

In some embodiments of the invention, to determine a gaze vector forperson 22 at a given time and position in FOV 30, responsive to valuesin the reference data array, 3D gaze tracker 20 acquires a range imageand picture of the person at the given time and position. Controller 24processes the range image and picture to identify and determine spatialcoordinates for eye and fiducial features of the person.

To determine head orientation of the person, the controller optionallydetermines an affine transformation of reference coordinates of fiducialfeatures that, in accordance with a best fit criterion, such as a leastsquares criterion, most closely reproduces the 3D spatial coordinatesdetermined for the fiducial features. A transformation of a headorientation associated with the reference coordinates by the affinetransformation provides the head orientation. A gaze vector directionrelative to the head orientation of the person is determined responsiveto coordinates of the eye features. The head orientation, gaze vectordirection, and a gaze vector origin, optionally determined from spatialcoordinates of the eye, define the gaze vector.

In some embodiments of the invention, controller 24 interpolatesreference data values responsive to spatial coordinates for eye andfiducial features of the person provided from the range image andpicture to determine a gaze vector for person 22.

In the above discussion, 3D gaze trackers are shown comprising a TOF 3Dcamera, which though sharing optical components with a picture camera isseparate from the picture camera. Embodiments of the invention are nothowever, limited to 3D gaze trackers having separate range and picturecameras, nor to TOF 3D cameras.

In some embodiments of the invention, a 3D gaze tracker comprises asingle photosensor, which is used to acquire both range images of aperson and pictures of the person. A shutter that shutters thephotosensor is controlled to shutter the photosensor open for exposureperiods to acquire range images of the person that have durations, whichare different from durations of exposure periods that the shutterprovides for acquiring pictures of the person.

And in some embodiments of the invention, a 3D gaze tracker comprises astereoscopic 3D imager that determines distances to features of a personin the 3D gaze tracker's FOV responsive to parallax exhibited by imagesof the features provided by two, spatially separated cameras in thesystem.

FIG. 6 schematically shows a stereoscopic 3D gaze tracker 250 comprisinga stereoscopic 3D imager 252 having two spatially separated cameras 254and 255 that acquire pictures (contrast images) of features in a FOV 256of the 3D gaze tracker from different perspectives. A controller 257 inthe stereoscopic 3D gaze tracker processes the pictures to identify andlocate eye and fiducial features and determine spatial coordinates tothe features responsive to distances to the features determined fromparallax that they exhibit in the pictures.

It is noted that whereas in the above description, a 3D gaze tracker inaccordance with an embodiment of the invention is used to interface aperson with a computer that interacts with the person via a videodisplay. However, embodiments of the invention are not limited tocomputers and systems that interface with a person via a video screen.For example, a smart “computerized” vending machine may comprise a 3Dgaze tracker in accordance with an embodiment of the invention todetermine which of a plurality of items the vending machine offers forsale a person wishes to buy. The 3D gaze tracker determines on which ofthe vending machine products the person's POR settles and in responsethe vending machine illuminates, for example, with an internal lightsource, the product to provide feedback to the person as to where thevending machine “thinks” the POR is located. If the POR remainssubstantially fixed on the product for a sufficient time after it isilluminated, the vending machine dispenses the product after paymentfrom the person is received.

In the description and claims of the present application, each of theverbs, “comprise” “include” and “have”, and conjugates thereof, are usedto indicate that the object or objects of the verb are not necessarily acomplete listing of components, elements or parts of the subject orsubjects of the verb.

Descriptions of embodiments of the invention in the present applicationare provided by way of example and are not intended to limit the scopeof the invention. The described embodiments comprise different features,not all of which are required in all embodiments of the invention. Someembodiments utilize only some of the features or possible combinationsof the features. Variations of embodiments of the invention that aredescribed, and embodiments of the invention comprising differentcombinations of features noted in the described embodiments, will occurto persons of the art. The scope of the invention is limited only by theclaims.

1. A system for interfacing a person with a computer: a video display onwhich the computer generates an image to interact with the person; a 3Dcamera that acquires a range image of the person located in a field ofview (FOV) of the camera; a picture camera that acquires a picture ofthe person in the FOV of the 3D camera; and a controller that processesthe range image and the picture to determine spatial coordinates forfeatures of the person's head and an eye of the person, determines agaze direction and origin for a gaze vector of the eye responsive to thedetermined spatial coordinates and modifies the image displayed on thevideo display responsive to the gaze vector.
 2. A system according toclaim 1 wherein modifying the displayed image comprises determining apoint of regard (POR) responsive to the gaze vector and modifying thedisplayed image responsive to the POR.
 3. A system according to claim 2wherein modifying the displayed image responsive to the POR comprisesgenerating an icon on the video display that indicates a location of thePOR in the display.
 4. A system according to claim 3 wherein the icon isconfigured to indicate a region of uncertainty (ROU) for the POR.
 5. Asystem according to claim 1, wherein the FOV extends from a distancefrom the gaze tracker equal to about 0.3 m.
 6. A system according toclaim 1, wherein the FOV extends to a distance from the gaze trackerequal to or greater than about 2 m.
 7. A system according to claim 1 andcomprising a light source that illuminates at least a portion of theFOV.
 8. A system according to claim 7 wherein the controller adjustsintensity of light provided by the light source responsive to a spatialcoordinate of the spatial coordinates determined by the controller.
 9. Asystem according to claim 7 wherein the controller adjusts direction oflight provided by the light source responsive to a spatial coordinate ofthe spatial coordinates determined by the controller.
 10. A systemaccording to claim 1, wherein the features comprise at least one featureof the person's eye for which spatial coordinates can be used todetermine gaze direction of the eye.
 11. A system according to claim 1,wherein the features comprise at least one feature of the person's headfor which spatial coordinates can be used to determine orientation ofthe head.
 12. A system according to claim 1, wherein the 3D cameracomprises a stereoscopic camera.
 13. A system according to claim 1,wherein the 3D camera comprises a time of flight (TOF) 3D camera.
 14. Asystem according to claim 1, wherein the displayed image is associatedwith a video game.
 15. A system according to claim 14 the video game isan online video game.
 16. A system for interfacing a person with a videogame: a video display on which images associated with the video game aredisplayed; a 3D camera that acquires a range image of the person locatedin a field of view (FOV) of the camera; a picture camera that acquires apicture of the person in the FOV of the 3D camera; and a controller thatprocesses the range image and the picture to determine spatialcoordinates for features of the person's head and an eye of the person,determines a gaze direction and origin for a gaze vector of the eyeresponsive to the determined spatial coordinates and modifies the imagedisplayed on the video display responsive to the gaze vector.
 17. Asystem according to claim 16 wherein modifying the displayed imagesresponsive to the POR comprises generating an icon on the video displaythat indicates a location of the POR in the display.
 18. A systemaccording to claim 16, wherein the features comprise at least onefeature of the person's eye for which spatial coordinates can be used todetermine gaze direction of the eye.
 19. A system according to claim 16,wherein the features comprise at least one feature of the person's headfor which spatial coordinates can be used to determine orientation ofthe head.
 20. A method of interfacing a person with a computer themethod comprising: acquiring a range image of a person that providesdistances to the person's features; acquiring a contrast image of theperson; processing the range and contrast images to provide a gazevector for the person; providing the computer with information relatedto the gaze vector; and indicating to the person a point of regarddetermined responsive to the gaze vector.